The present invention refers to sealing apparatus and, more particularly, to the heat sealing of thermoplastic tubular members such as collapsible dispensing tubes.
Conventional dispensing tubes in toothpaste and the like are commonly made of plastic materials. The preparations are usually injected into the tubes through an unseated end opposite that of the dispensing region which is often tapered to a narrow diameter and capped. After the tube has been filled, the end through which the filling took place must be closed and sealed to prevent the contents from leaking out. This is particularly a problem with more viscous pastes in that the considerable pressure applied to the tube to extrude it through the capped end also bears against the sealed end. Although the formation of solid joints is no longer a technical problem with the advent of improved thermoplastic resins and polyethylene synthetic resins, the manner and efficiency in which such joints are formed is an ever present consideration. For example, certain materials such as polyethylene cannot be sealed by the direct application of hot sealing elements or sticking is the result. Therefore, prior art technology has produced radiant heater-squeezing assemblies which effectively form leak-tight seals across tubular orifices and related open material plies.
The methods and apparatus for forming seals in thermoplastic materials have been well defined by prior art patents. For example, U.S. Pat. No. 2,691,474 to Olson discloses a thermoplastic sealing structure. The Olson apparatus teaches the uniting of polyethylene plies with radiant heat and subsequent squeezing until the material sets. A manually operable machine is likewise disclosed incorporating means for clamping the material to be sealed in one step, providing means for heating the heating element and subsequently lowering it to close proximity with the plastic to be sealed. The operator then rotates separate handles after releasing the heating element to press the molten plastic into a seal. Other such prior art methods and apparatus known to the inventor hereof are as follows:
______________________________________ U.S. PAT. NO. DATE ISSUED INVENTOR ______________________________________ 2,928,216 3/15/60 R. Orsini 2,524,584 10/03/50 W. J. Zehr 2,987,858 6/13/61 W. C. Kerker 3,333,391 8/01/67 J. M. Horeth et al 4,019,305 4/26/77 Russell P. McGhie et al ______________________________________
As the above references reflect, the formation of a leak-tight seals in plastic tube containers is of utmost importance for obvious sanitary and commercial reasons. Likewise, performance consistency is critical and it is made no more apparent than in the smaller "manual" tube sealing operations. The forming of a "good" joint in heat sealable plastic depends upon such factors as heat intensity, heat duration, and the equally important collateral aspects of alignment, positioning and the "squeeze" time of the heated molten plastic. Such parameters are not easy to maintain with most conventional apparatus, particularly where the operator must actuate a plurality of handles and/or tie up both hands in performing the required operations.
It is a purpose of the present invention to overcome the disadvantage of the prior art methods and apparatus by providing a system utilizing a single drive train for "programmed" control of the sealing stages even with manual actuation. The methods and apparatus as disclosed herein provide a radiant heating element which is constantly on at a preselected temperature and engagable with the material to be sealed only through a sequentially staged progression necessitating only one hand of the operator. In this manner, the operator has one hand free to handle product and concentrate on performance accuracy with few of the associated problems of earlier methods of multi-operational stage procedures. In addition, the incorporation of semi-automated operation is made feasible with a system depending substantially on single rotational speed consistency as its main quality control consideration.